[0001] The present invention relates to improved abrasive grain and a method of making the
same. The improved abrasive grain are useful in abrasive products.
[0002] The abrasives industry generally concerns abrasive products comprising binder and
a plurality of abrasive grains which are used to abrade a workpiece (e.g., stainless
steel). Desirable abrasive grains are hard, tough, and chemically resistant to the
workpiece being abraded. The hardness property is associated with the abrasive grain
not yielding from forces of grinding and not dulling. The toughness property is associated
with strength and fracture resistance of the abrasive grain.
[0003] In general, it is known that inclusion of various materials within an alpha alumina
based abrasive grain will modify the characteristics of the grain. What has been sought
is improvement with respect to hardness and toughness.
[0004] The present invention relates to the subject-matter disclosed in the claims.
[0005] According to preferred applications of the present invention, there is provided an
alumina based ceramic abrasive grain. The abrasive grain has an average hardness of
at least about 21 GPa (preferably at least about 22 GPa) and an average toughness
of at least about 4 MPa·m
½. The abrasive grain comprises a sintered product of precursor material including
therein alumina, zirconia, and rare earth oxide. Preferred ceramic abrasive grain
according to the present invention are formed from precursor material comprising yttria
and magnesium oxide (and/or precursor(s) thereof) therein.
[0006] Preferably, the precursor grit material to the sintered product comprises, by weight
on an elemental oxide basis, about 70 to about 95% alumina; about 0.1 to about 15%
zirconia; and about 0.1 to about 10% rare earth metal oxide. In addition, the precursor
grit material preferably comprises about 0.1 to about 10% yttria and about 0.3 to
about 10% magnesium oxide. A most preferred alumina based ceramic abrasive grain according
to the present invention is formed from a grit material comprising by weight about
85 to about 93% alumina, about 0.5 to about 8% zirconia, about 0.5 to about 10% (preferably
about 0.5 to about 5%) rare earth metal oxide, about 0.1 to about 3% yttria, and about
0.3 to about 1.5% magnesium oxide. Preferred rare earth oxides include oxides of lathanum,
praseodymium, samarium, neodynium, cerium, and dysprosium.
[0007] The method may include preparing a dispersion having nucleating material therein.
The term "nucleating material" as used herein refers to a nucleating agent or precursor
thereof. The method may also involve a step of including a metal oxide precursor (modifier
precursor) within the dispersion.
[0008] The base grits formed from the dispersion may be treated, for example, by coating
with metal oxide (modifier precursor) precursor prior to sintering.
[0009] The ceramic abrasive grain according to the present invention comprises alumina,
and, by weight on an elemental oxide basis, about 0.1 to about 15% zirconia, and about
0.1 to about 10% a metal oxide selected from the (a) yttria; (b) a rare earth oxide
selected from the group of consisting of oxides: ytterbium, neodymium, lanthanum,
praseodymium, samarium, gadolinium, cerium, dysprosium, erbium, and mixtures thereof;
and (c) mixtures thereof, wherein said alumina preferably is present as one of alpha
alumina, alumina reaction product(s), or a combination thereof, said zirconia preferably
is present as one of zirconia, zirconia reaction product(s), or a combination thereof,
and said metal oxide preferably is present as one of a metal oxide, a metal oxide
reaction product(s), or a combination thereof, and wherein said abrasive grain has
an average hardness of at least about 21 GPa and an average toughness of at least
about 4 MPa·m
½.
[0010] The term "reaction product(s)" as used herein refers to oxide(s) that form between
two or more metal oxides. For example, alumina and magnesium oxide, if present, may
react to form spinel; alumina, magnesium oxide, if present, and lanthanum oxide, if
present, may react to form LaMgAl
11O
19; and titanium oxide, if present and magnesium oxide, if present, may react to form
MgTi
2O
4. LaMgAl
11O
19 is an example of each of an alumina reaction product, a magnesium oxide reaction
product, and a lanthanum oxide (rare earth oxide) reaction product. Further, spinel
is an example of a reaction product that is both an alumina reaction product and a
magnesium oxide reaction product.
[0011] Preferred abrasive products according to the present invention comprise a sintered
product having equiaxed zirconia particles distributed therein (preferably evenly
distributed between alpha alumina crystallites), with the majority of zirconia particles
having a diameter up to about 0.4 µm (preferably less than about 0.1 µm). Preferably,
the alpha alumina is present as crystallites having a size up to about 1 µm and typically
up to about 0.5 µm. The term "size" in this context is meant to refer to the longest
dimension of the particles or crystallites to which reference is being made.
[0012] In addition, components are preferably provided such that in combination with a divalent
metal 5 cation and the aluminum ion, the rare earth metal will form a preferred reaction
product according to the formula MLnAl
11O
19 wherein O is oxygen; M is a divalent metal cation; Ln is a rare earth metal ion (in
the +3 oxidation state); and Al is aluminum ion. Preferably, the sintered product
(i.e., abrasive grain) is formulated to contain about 5 to about 30% by weight of
the MLnAl
11O
19.
[0013] The present invention includes within its scope abrasive articles having therein
abrasive grain material according to the present invention.
[0014] The present invention also includes within its scope a preferred process for preparing
abrasive grain material.
[0015] The drawings comprise a part of the specification and include therein exemplary embodiments.
In the drawings, relative material thicknesses may be shown exaggerated to facilitate
an understanding of the invention.
[0016] FIG. 1 is a fragmentary cross-sectional schematic view of a coated abrasive product,
incorporating therein abrasive grains according to the present invention.
[0017] FIG. 2 is a perspective view of a bonded abrasive product incorporating abrasive
grainsaccording to the present invention.
[0018] FIG. 3 is an enlarged, fragmentary, schematic view of a nonwoven abrasive product
incorporating abrasive grains according to the present invention.
[0019] FIG. 4 is a scanning electron photomicrograph of an abrasive grain prepared according
to Example 33 and taken at 25,000X.
[0020] The present invention relates to alpha alumina based abrasive grains. According to
the invention, there is provided within alpha alumina based abrasive grains certain
additional components which provide for improved characteristics. In addition, the
invention concerns methods of preparing such improved abrasive grains, and improved
abrasive products which include an effective amount of the improved abrasive grains
therein.
[0021] Herein the term "abrasive grain" or variants thereof is used to refer to the granular
abrasive material after it has been prepared (sintered) for inclusion in an abrasive
product. The term "base grit" or "base grit material" is used to refer to alumina
based ceramic grain precursor which, when sintered, or calcined and sintered, provides
abrasive grain according to the present invention. Calcined and uncalcined base grit,
as described herein, typically have sufficient porosity to allow a liquid (e.g., water
or an organic solvent) to impregnate the pores through capillary action.
[0022] In general, the present invention comprises providing an alumina based abrasive grain
precursor with an effective amount of at least one rare earth oxide and an effective
amount of zirconia therein in a preferred manner. When such a base grit is sintered
to form a ceramic product, an improved abrasive grain results.
The Base Grits
[0023] In general, the base grits are prepared according to a process including the steps
of: (a) preparing a dispersion of alumina hydrate, and (b) drying the dispersion to
form dried porous solid (base grit material). From the dried porous solid, abrasive
grain material is generated by sintering. Typically, the dried porous solid is calcined
to provide a porous precursor grit. During the process, zirconia and rare earth oxide(s)
are provided in the porous solid to generate improved grains.
[0024] In general, the base grit material can either be initially formed (e.g., from a dispersion)
with zirconia and/or rare earth oxide(s) included therein; or the base grit material
can be modified to incorporate such materials therein. Characteristics of the resulting
abrasive grains can be modified by such variations.
[0025] Preferred base grit material for utilization as particles in processes according
to the present invention are prepared according to modifications of known sol-gel
processes. Known processes, for example, are disclosed in U.S. Pat. Nos. 5,011,508
(Wald), 4,744,802 (Schwabel), 4,623,364 (Cottringer), 4,574,003 (Gerk), 4,518,397
(Leitheiser et al.), and 4,314,827 (Leitheiser). Modifications to the processes in
order to achieve the improved product of the present invention are indicated herein.
The processes concern formation of a dispersion of the alumina, followed by gelation,
drying and (optionally) crushing.
[0026] In general, to prepare the alumina base grits by a sol-gel process, a dispersion
comprising from about 2 to about 60 percent by weight alpha aluminum oxide monohydrate
(typically boehmite) is formed, although other hydrates may be used. The weight percent
is based on a total of hydrate plus liquid carrier, without regard to adjuvants or
additives. The boehmite can be prepared from various conventional techniques or it
can be acquired commercially. Commercially available boehmite usable in sol-gel processes
as described herein include: Disperal®, available from Condea Chemie GmbH of Hamburg,
Germany, and Catapal®, available from Vista Chemical Co., Houston, TX. These aluminum
oxide monohydrates are in alpha form, are relatively pure (including relatively little,
if any, hydrate phases other than monohydrate), and have high surface area.
[0027] Although the liquid carrier may be a non-polar organic carrier (e.g., heptane or
hexane), the liquid carrier is typically water, preferably, deionized water. Generally,
the dispersion (with respect to all components) contains at least about 10% by weight
liquid carrier, preferably, between about 30 and about 80% by weight liquid carrier.
[0028] A peptizing agent may be used in the boehmite dispersion to produce a more stable
hydrosol or colloidal dispersion. Monoprotic acids which may be used as the peptizing
agent include acetic, hydrochloric, formic, and nitric acids. Nitric acid is the preferred
peptizing agent. Multiprotic acids are normally to be avoided because they tend to
rapidly gel the dispersion, making it difficult to handle or mix in additional components.
Some commercial sources of boehmite contain an acid titer (e.g., acetic, formic, or
nitric acid) to assist in forming a stable dispersion.
[0029] The dispersion may contain a precursor or modifying additive (modifier) which is
added to enhance some desired property of the finished product or to increase the
effectiveness of a subsequent processing step, such as sintering. Such modifiers are
generally introduced in the form of a modifier precursor to an oxide (typically a
metal salt material which is a precursor to the corresponding oxide; conversion being
accomplished upon application of heat during calcining) soluble in a liquid carrier.
They typically comprise water soluble salts. Mixtures of modifiers or modifier precursors
may be utilized. Examples of suitable water soluble salts include metal salt precursors
(e.g., nitrates and acetates) for oxides of iron, titanium, magnesium, zinc, nickel,
silicon, hafnium, and mixtures thereof.
[0030] The pH of the dispersion affects how fast the dispersion will thicken or gel. Typically,
the pH should be in the range of about 1.5 to about 4. In general, the lower the pH,
the higher the rate of gelation. The addition of the modifier precursor generally
results in gelation of the dispersion.
[0031] The dispersion may contain a nucleating material in an amount effective to enhance
the transformation to alpha alumina. Suitable nucleating materials include fine particles
of alpha alumina, alpha ferric oxide or its precursor, titanates or their precursors,
chromium oxide or its precursor, and other materials which can nucleate the transformation
of the base grits during sintering. Nucleating such dispersions is disclosed, for
example, in U.S. Pat. Nos. 4,774,802 (Schwabel), 4,623,364 (Cottringer), and 4,964,883
(Morris).
[0032] Shaping of the gel, which is optional, may be accomplished by conventional means
such as pressing, molding, cutting, or extrusion, with air drying. It may be done
in steps, for example, by first forming plastic mass of the partially dried dispersion
through extrusion. Examples of shaped abrasive grains include rods, pyramids, cones,
triangles or spheres. Irregularly shaped abrasive grain products are conveniently
formed by depositing a partially dried dispersion in any convenient size and shape
of drying vessel (e.g., a pan-shaped vessel) and drying, typically at a temperature
below the frothing temperature of the dispersion.
[0033] Whether shaped or not, the dispersion is generally dried to form a base grit material.
Air drying steps may be used for removal of free water from the dispersion to form
the grit material. Drying can be accomplished, for example, in a forced air oven at
a temperature in the range of about 50°C to about 200°C, preferably between about
75°C and about 125°C. Generally, the gelled dispersion is heated slowly during drying
to inhibit frothing.
[0034] After the gel is dried, it may be crushed or shaped through any suitable means. Examples
of crushing techniques include use of a hammer mill, ball mill, or a roll crusher.
Any method of comminuting the solid can be used, and the term "crushing" is meant
to refer to any such method. In general, a wide variety of particle sizes, i.e., about
10 to about 4000 micrometers, may be used as base grits. Generally a selected size
range is isolated for any given use. Classification steps such as screening may be
used to obtain selected particle sizes or size fractions. It is noted that sintering,
or calcining and sintering, generally leads to particle shrinkage on the order of
about 33% of linear dimension. This should be taken into consideration during fraction
selection.
[0035] The crushed or shaped material may in some instances comprise the base grits or base
grit material. In other instances, the crushed or shaped material will comprise a
"grit precursor," the base grit material being formed by calcining the material or
providing other modifications thereto. In typical applications, it will be preferred
to calcine the base grit material to remove water or other volatiles. If the grits
are formed using a non-polar organic solvent as the liquid carrier, a calcining step
is typically not needed.
[0036] During calcining, essentially all the volatiles are removed from the precursor by
heating the precursor to a temperature between about 400°C and about 1000°C (preferably
about 400°C to about 800°C). The base grit material is held within this temperature
range until the free water and preferably over about 90 weight percent of any bound
volatiles are removed.
Incorporation of Zirconia and Rare Earth Metal Oxide(s) into the Base Grits
[0037] According to the present invention, the base grits are modified to advantage by the
inclusion therein of zirconia and rare earth metal oxide(s). The step of modification
with respect to each component (independently or together) can be conducted either
during base grit formation or following base grit formation. In addition, both types
of components can be introduced via both means if desired.
[0038] The average hardness is measured according to the American Standard Test Method (ASTM)
Standard E384 ("Standard Test Method for Microhardness of Materials,"
1991 Annual Books of ASTM Standards, Sec. 3, Vol. 3.01, p. 463) with a 500 gram load. The average toughness is measured
according to the test procedure outlined in the article "Equilibrium Penny-like Cracks
in Indentation Fracture," by Lawn and Fuller,
J. of Mat. Sci., Volume 10, (1974), pp. 2016-24. According to preferred applications of the present
invention, abrasive grains are provided which have an average hardness of at least
about 21 GPa (preferably at least about 22 GPa) and an average toughness of at least
about 4 MPa·m
½.
[0039] In typical applications, improvement will be found if the base grit material is provided
with sufficient amounts of the components so that the sintered ceramic abrasive grain
which results comprises: about 70 to about 95% by weight, preferably about 85 to about
93%, alumina; about 0.1 to about 15%, preferably about 0.5 to about 8%, zirconia;
and about 0.1 to about 10%, preferably about 0.5 to about 5%, rare earth oxide(s).
In addition preferred abrasive grain include less than about 10%, preferably about
0.1 to about 3%, yttria; and, about 0.5 to about 10%, preferably about 0.3 to about
1.5%, magnesium oxide. The rare earth oxide(s) can be selected from oxides of: praseodymium,
samarium, ytterbium, neodymium, lanthanum, gadolinium, cerium, dysprosium, erbium,
and mixtures thereof. In this context, when it is said that the abrasive grain includes
these various materials by weight percent, reference is meant to the final sintered
ceramic abrasive grain, and the weight percent is stated on an elemental oxide basis
without regard to the phases present and without regard to the presence of any coating
on the grain. Thus, should the abrasive grain be coated, the weight percent should
be based upon or calculated based upon the grain minus the weight of the coating;
i.e., the sintered core.
[0040] A variety of methods may be utilized to introduce the various minor (weight percent)
components, i.e., non-alumina components, into the base grits. While any of the methods
disclosed generally result in improved base grits, variations in the methods used
will lead to variations in the characteristics of the final sintered product.
[0041] With respect to zirconia introduction, in general, the zirconia may be introduced
by any one of three methods, or a combination of these methods. The first general
method is the provision of zirconia sol in the dispersion of aluminum oxide monohydrate
during the base grit formation, either by zirconia sol addition to the dispersion
or by mixing zirconia particles into the dispersion in a manner such that zirconia
sol formation results. The second involves the introduction of a zirconia precursor
(e.g., a zirconium salt) into the dispersion of aluminum oxide monohydrate during
the base grit formation. The third involves introduction of a zirconia precursor (zirconium
salt) into porous base grits after their formation through impregnation. Preferably,
the zirconia is introduced as a zirconium component during base grit formation either
as zirconia particles in the dispersion or as a zirconium salt (precursor to zirconia)
provided in the dispersion. In general, the rare earth metal oxides, magnesium oxide,
and yttria (if used) are introduced into the base grits by either or both of the latter
two processes described for zirconia (i.e., either through introduction of salt precursors
of these materials into the dispersion during the sol-gel process, or impregnation
of already formed base grits with the appropriate salts). Preferably, the rare earth
metal oxide salt precursor is introduced by impregnation of the base grit material.
A reason for this is that if the rare earth metal oxide precursor is introduced during
the sol-gel process (i.e., in the dispersion of zirconia or zirconia precursor and
alumina precursor) migration of the rare earth salt(s) during drying may lead to nonuniform
dispersion of the rare earth oxide(s) in the resulting base grit material.
[0042] A preferred means for incorporating ceria into the abrasive grain is disclosed in
WO 94/07970.
[0043] When metal salts (metal oxide precursors including zirconium salts) are utilized,
in general, the oxide of the metal will result after drying and calcining of the resulting
particles. That is, herein the term "oxide precursor" or variants thereof is used
to refer to a salt (e.g., a nitrate salt) which, upon exposure to heat, is converted
to corresponding oxide.
[0044] Introduction of metal oxide precursor(s) into the sol-gel is merely a matter of mixing
an appropriate oxide precursor (metal salt) into the dispersion. The zirconia precursor
may be, for example, a zirconyl alkylate, typically, zirconyl formate or zirconyl
acetate. Such salts are water soluble and, thus, can be readily mixed into the dispersion
in the sol-gel process, provided the liquid carrier is water.
[0045] Rare earth oxide precursors may be the appropriate metal salt of a volatile anion,
for example, nitrates, formates, and acetates. The most readily available chemical
forms of rare earth metals are typically the oxides, which are converted to the salts
(modifier precursors) by reaction with an excess of concentrated nitric acid to produce
a nitrate solution. The nitrate solution can be readily introduced into the dispersion
of the sol-gel process through mixing. Similar processes can be used, for example,
to provide the dispersion of the sol-gel process and, thus, the base grits ultimately
formed with oxide precursors of yttria, magnesium oxide, zinc oxide, cobalt oxides,
nickel oxides, hafnia, chromium oxides, and mixtures thereof therein.
[0046] A preferred material for certain applications results if: the zirconia addition occurs
during the sol-gel process so that an even distribution of zirconia throughout the
resulting ceramic grain is achieved; and the rare earth metal oxide addition (and
any other oxide addition) occurs through impregnation of the base grit material. In
this manner, the product will have relatively even distribution of zirconia throughout.
[0047] The most preferred method for incorporating zirconia into the abrasive grain is disclosed
in WO 94/07809.
[0048] In general, calcined base grits prepared according to the sol-gel process are porous;
i.e., they generally have pores about 700-900 nanometers in size (diameter) extending
therein from an outer surface. When mixed with a liquid carrier (preferably water,
more preferably deionized water) containing dissolved metal salt therein, the metal
salt can impregnate the pores through capillary action. When dried and calcined, the
impregnate (metal oxide precursors) will be converted to metal oxide(s).
[0049] In general, all that is required for introduction of metal oxide precursor through
the impregnation process is a mixing of an appropriate amount of carrier liquid with
the base grits. Generally, enough liquid carrier should be used to give substantial
saturation (at least about 70% saturation) of the grits. When the base grits are prepared
according to the sol-gel process described above, at least about 50 ml and, preferably,
at least about 60 ml of liquid carrier with impregnate dissolved therein. should be
mixed with each 100 grams of base grits. If the ratio is within the 50 to 60 ml per
100 gram range as stated, in general all of the dissolved metal oxide precursor will
impregnate the base grits, i.e., excess solution is preferably avoided. From the above
descriptions, it will be understood that when impregnation is used, the modifier(s)
(or modifier precursor(s)) will be preferentially partitioned toward outer parts of
the abrasive grains. Introduction of various materials into base grits by an impregnation
process is generally described in U.S. Pat. No. 5,164,348.
[0050] As indicated above, zirconia may be introduced into the base grits during the sol-gel
process by mixing of a zirconia sol into the alumina-hydrate dispersion. A zirconia
sol is a dispersion of colloid zirconia particles in a liquid medium. The liquid medium
can be water (preferably deionized water) or a non-polar organic carrier (e.g., heptane
or hexane), however, it is generally preferred that a majority (greater than 50% by
weight) of the liquid medium be water (preferably deionized water). The zirconia sol
should contain, by weight, between about 5 and about 60%, preferably between about
15 and about 40%, colloidal zirconia particles. It is preferred that the particle
size be at least about 97% by weight and preferably about 100% by weight less than
about 0.1 micrometer, preferably, with at least about 90% by weight less than about
0.05 micrometer and at least about 50% by weight less than about 0.02 micrometer.
[0051] The pH of the zirconia sol prior to addition to the dispersion is typically less
than about 5, preferably less than about 4. The zirconia sol may contain some nitric
or acetic acid as stabilizers. When this method is practiced, the dispersion formed
in the sol-gel process comprises both alumina sol and zirconia sol. The preferred
range of percent solids of the zirconia in the dispersion with the alumina is between
about 5 and about 30 percent.
Conversion of the Base Grits to Improved Abrasive Grain
[0052] According to the present invention, the base grit are converted into improved abrasive
grain through application of one or more treatments. A principal step of conversion
is sintering of the base grit to form ceramic abrasive grain comprising alumina, zirconia,
and rare earth metal oxide. However, further modifiers, nucleating materials, and/or
coating may be added to the base grit. The base grit may be improved by more than
one of these referenced treatments.
A. Sintering of the Abrasive Grain Precursor
[0053] The base grit material, including the alumina, zirconia, rare earth metal oxide,
and any other modifier and/or nucleating material and/or coating thereon, comprises
the precursor to the ceramic abrasive grain. Upon sintering, the grits (grit material)
or precursor form a unique and improved abrasive grain.
[0054] Sintering of the abrasive grain may be accomplished through a variety of conventional
processes. Typically, the sintering will be conducted at a temperature between about
1200°C and about 1650°C for a sufficient period of time to complete the conversion
of the precursor. Generally, the sintering step comprises the conversion of alumina
to alpha alumina (or alpha alumina and reaction product of alumina with metal oxide
modifier(s)). Although the length of time to which the base grits should be exposed
to sintering temperatures may be varied depending upon factors such as the precise
composition of the grit, generally sintering can be accomplished within a time period
of a few seconds to about 120 minutes. The sintering of various types of base grits
is described in general in U.S. Pat. No. 4,314,827 (Leitheiser et al.). The techniques
of sintering described in that reference may be applied to grits prepared according
to the present invention.
B. (Optional) Impregnation of the Base Grits With Modifier Prior to Sintering; Nucleation;
Coating
[0055] Preferred characteristics can be imparted to the sintered product by impregnating
the base grits with still further metal oxide modifier precursor (in addition to rare
earth metal oxide precursor and/or zirconia precursor). The impregnation procedure
described generally above may be utilized. These metal oxide modifiers described with
respect to the sol-gel process may be used.
[0056] A nucleating material may be added to the base grits to result in a seeded microstructure
in the outer portion of the base grit during firing. The nucleating material may be
added by treating the base grits with a liquid medium having the nucleating material
carried therein. The treatment may be conducted simultaneously with impregnation.
[0057] The abrasive grains of the present invention may further comprise a surface coating,
i.e., a coating covering the sintered core. Typically, the coating will comprise metal
oxide, most typically zirconia, silica, or alumina (e.g., alpha alumina, transitional
alumina, or hydrated alumina). Any of a variety of coating methods may be utilized,
including the ones described in U.S. Pat. Nos. 5,011,508 (Wald), 1,910,440 (Nicholson),
3,041,156 (Rowse), 5,009,675 (Kunz), 4,997,461 (Markhoff-Matheny), and 5,042,991 (Kunz).
The preparation of the coating may include the use of nucleating material. In some
instances, a preferred coating not described in the above-cited references may be
applied to the base grits by addition of a dispersion or suspension carrying inorganic
particulates (typically metal oxides) therein to the base grits. A coating formed
from inorganic particulates in this manner is described in Assignee's U.S. Pat. No.
5,213,591. An alternative coating, formed from metal alkoxides, is described in WO
94/02560.
The Resulting Abrasive Grain
[0058] Selected preferred abrasive grains according to the present invention are depicted
in the electron photo-micrograph of FIG. 4. The photomicrograph of FIG. 4 is a cross-sectional
view of an example of abrasive grain according to the present invention (Example 33).
The abrasive grain sample depicted was first polished to a one micrometer finish and
then thermally etched for 15 minutes at 1250°C. The sample was then examined in the
scanning electron microscope at 25,000x magnification. The microstructure comprises
an alpha alumina matrix comprising alpha alumina crystallites, and within the matrix
are a plurality of platelets and equiaxed zirconia particles. The platelets are primarily
a magnetoplumbite structure according to the formula: MLnAl
11O
19, where M is divalent metal cation such as a magnesium cation; Ln is rare earth ion
(e.g., in a +3 oxidation state) (e.g., cation of praseodymium, samarium, ytterbium,
neodymium, lanthanum, cerium or erbium); O is oxygen; and Al is aluminum ion. The
platelets are randomly distributed in the alumina matrix (between alpha alumina crystallites
and zirconia particles). The diameter of the platelets is generally up to about 1
µm. The thickness of the platelets is between 0.04 and 0.08 µm, usually about 0.04
to about 0.06 µm. The volume of the platelets can range from about 5 to about 50%
of the microstructure. Usually the platelets comprise between about 25% and about
35% of the core volume. The volume percentages are greatly dependent upon the abrasive
grain formulation.
[0059] The equiaxed zirconia particles generally have a diameter less than about 0.1 µm,
usually between about 0.01 and about 0.04 µm, and most typically about 0.02-0.03 µm.
The zirconia particles are distributed between alpha alumina crystallites. The term
"equiaxed" as used in this context means that each zirconia particle is shaped with
an extension of approximately equal amount from a central point. Thus, each zirconia
particle is roughly spherical.
[0060] The microstructure depicted in FIG. 4 exhibits some unique properties with respect
to abrasive grain behavior. In particular, the presence of both platelets and zirconia
particles leads to a tough abrasive grain. Although not wishing to bound by any theory,
it is believed that the presence of the platelets inhibits crack propagation through
the sample.
[0061] It is also believed that the presence of 5 zirconia in an alumina system, as well
as the particle size of the zirconia and the volume present, greatly enhances the
mechanical properties of the resulting abrasive grains. Zirconia particles appear
to not only toughen the abrasive grain, but also to improve the microstructure by
hindering grain growth in alumina and alumina reaction products. Thus, it is theorized
that the addition of zirconia alters the alumina microstructure and aids in densification.
The toughness can be attributed (in some compositions) to the utilization of tetragonal
to monoclinic transformation concept of the precipitated or the dispersed zirconia
particles. The strength increase by the zirconia addition is therefore the combined
effects of toughness increase and microstructural improvement. It is also theorized
that the addition of rare earth oxide(s) aids in the stabilization of tetragonal or
cubic zirconia phases in some compositions.
[0062] Preferred abrasive grains, as indicated previously, are both hard and tough. These
properties are associated with achievement of the microstructure described in the
previous three paragraphs. In general, the hardness property is associated with resistance
of the grain to yielding from the forces of grinding. The toughness property is associated
with strength and fracture resistance. If an abrasive grain is relatively hard, but
not sufficiently tough, then the grain will tend to fracture prematurely during abrading,
i.e., a reduced useful lifetime results. On the other hand, if the abrasive grain
is relatively tough but not hard, then it will rapidly dull during abrading, i.e.,
it will exhibit reduced abrading performance. Although hardness and toughness properties
are often considered to be inversely related (i.e., increase in hardness leads to
decrease in toughness and
vice versa) in systems according to the present invention both properties are achieved at desirable
levels.
Abrasive Products
[0063] The present invention includes within its scope the provision of abrasive products
having improved abrasive grains therein. Preferably, the abrasive grains will have
been prepared according to processes described herein and comprise the sintered product
of base grit having the appropriate metal oxide or metal oxide precursors therein.
Again, the abrasive grain may have been formed with a nucleating agent present and/or
with a coating, as generally described.
[0064] One type of abrasive product according to the present invention comprises a backing
(substrate) with abrasive grains, as described herein, adhered thereto by binder.
The backing may be cloth, polymeric film, fiber, nonwoven web, paper, combinations
thereof, or treated versions thereof. A variety of inorganic or organic binders can
be utilized. The abrasive grains may be applied in one layer or in a plurality of
layers. A preferred method of making coated abrasives is described in U.S. Pat. Nos.
4,734,104 (Broberg) and 4,737,163 (Larkey).
[0065] An example of a coated abrasive product is provided in FIG. 1 at reference numeral
1. Referring thereto, backing (substrate) 2 has abrasive layer 3 comprising abrasive
grain 4 secured to a major surface of backing 2 by make coat 5 and size coat 6. In
some instances a supersize coat, not shown, may be used.
[0066] Bonded abrasive products (e.g., grinding wheels and cutoff wheels) according to the
present invention generally comprise shaped masses of abrasive grain, described herein,
held together by a binder. Conventional binders for grinding wheels include organic,
metallic, or vitrified binder. In FIG. 2, grinding wheel 10 is depicted comprising
abrasive grain 11 molded in a wheel and mounted on hub 12. For additional details
in the preparation of grinding wheels see, for example, U.S. Pat. No. 4,997,461 (Markhoff-Matheny).
Cutoff wheels can be made using conventional techniques known in the art. Binders
for cutoff wheels include organic binder.
[0067] Nonwoven abrasive products incorporating abrasive grains according to the present
invention typically comprise an open porous lofty polymer filament structure having
the abrasive grains of the invention distributed throughout the fiber structure and
bonded therein by an organic binder. Typical fibrous filament structures usable with
such constructions comprise polyamides, polyesters, and polypropylenes. In FIG. 3,
a schematic depiction, enlarged about 100x, of a typical nonwoven abrasive article
is provided. The article comprises fibrous mat 50 as a substrate onto which abrasive
grain 52 are adhered by binder 54. For additional details in the preparation of nonwoven
abrasive products see, for example, U.S. Pat. No. 2,958,593 (Hoover et al.).
[0068] As indicated generally above, abrasive products according to the present invention
generally comprise binder and abrasive grains or particles therein. A wide variety
of binders may be used in abrasive products according to the present invention, including
conventional ones. Useful binders include phenolic, urea-formaldehyde, melamine-formaldehyde,
polyester resins, glue, aminoplast resins, epoxy resins, acrylate resins, urethane
resins and combinations thereof. The binder may also include inorganic particulate.
Such particulates can be grinding aids or fillers. Examples of such grinding aids
include cryolite, ammonium cryolite, potassium tetrafluoroborate, polyvinyl chloride,
sulfur and sodium chloride. Examples of fillers include calcium carbonate, silica
and calcium metasilicate.
[0069] Abrasive products or articles according to the present invention may contain, as
particulate material therein, 100% abrasive grains which have been improved according
to the descriptions herein. In addition, or alternatively, the abrasive articles may
contain a blend of abrasive grains according to the present invention with other types
of abrasive grains or diluent grains. Conventional abrasive grains usable in this
fashion include fused aluminum oxide, silicon carbide, garnet, diamond, cubic boron
nitride, fused alumina-zirconia, and other sol-gel abrasive grains. Diluent grains
include marble, gypsum, and glass. Abrasive grains according to the present invention
may be combined with abrasive agglomerates (see, e.g., U.S. Pat. No. 4,799,939 (Bloecher
et al.)).
[0070] Objects and advantages of this invention are further illustrated by the following
examples, but the particular materials and amounts thereof recited in these examples,
as well as other conditions and details, should not be construed to unduly limit this
invention. All parts and percentages are by weight unless otherwise indicated.
EXAMPLES
[0071] For all of the examples, the abrasive grains were made according to one of the Procedures
outlined below. All abrasive grain formulations are based upon weight on an elemental
oxide basis. After the abrasive grains were made, they were employed in a coated abrasive
fibre disc which was made according to the described procedure. The resulting coated
abrasive disc was tested according to a Test Procedure described below. For Examples
1 to 47, the preparation of the abrasive grain did not include the use of a nucleating
material, i.e., the abrasive grains were unseeded.
[0072] The weight percent figures given herein for abrasive grains are calculated on an
elemental oxide base without regard to the phases (e.g., reaction product(s)) present.
General Procedure I for Making the Abrasive Grains
[0073] The following were charged (with continuous mixing) into an 18.9 l polyethylene lined
steel vessel to form a dispersion, 2269 parts of room temperature deionized water,
45 parts of 16N analytical reagent grade nitric acid and 643 g of alpha aluminum oxide
monohydrate powder sold under the trade designation Disperal®. The resulting mixture
was dispersed at high speed for 3 to 4 minutes using a Giford-Wood Homogenizer Mixer
(Greeco Corp., Hudson, NH). The resulting sol was poured into a 46 cm by 66 cm by
5 cm polyester lined aluminum tray where it was dried in a forced air oven at 100°C
for about 24 hours to a friable solid. The resulting dried material was crushed using
a "Braun" type UD pulverizer having a 1.1 mm gap between the steel plates to form
particles. The particles were screened between 0.125 to 1 mm screen size. The retained
particles were fed into a rotary kiln to form calcined particles. The rotary kiln
was a 16 cm diameter, 140 cm long stainless steel tube having a 40 cm 600°C hot zone.
The tube was inclined at a 2.4 degree angle with respect to the horizontal. The tube
rotated at about 6 rpm to provide a residence time within the kiln of about 4 to 5
minutes.
[0074] The impregnation solutions were prepared with deionized water. The magnesium nitrate
solution was about 11% solids on an oxide basis. The yttrium nitrate solution was
about 23% solids on an oxide basis. The lanthanum nitrate solution was about 28% lanthanum
solids, and the cerium nitrate solution was about 39% solids on an oxide basis.
[0075] For each impregnation step, there was approximately twice as much by volume of the
calcined particles to the impregnation solution. The impregnation solution and the
calcined particles were thoroughly mixed together to cause the solution to be impregnated
into the calcined particles by capillary action. If a zirconia precursor was present
in the impregnating solution, then a vacuum was utilized in addition to the mixing
to cause the zirconia precursor to impregnate into the calcined particles. The resulting
impregnated particles were dried and then the dried particles were fed into the rotary
calciner as described above. For multiple impregnations, the calcined particles were
allowed to cool and then they were impregnated again with the desired impregnation
solution and calcined again.
[0076] Next, the calcined, impregnated particles were fed into a 1400°C rotary kiln. The
kiln was an 8.9 cm diameter, 1.3 meter long silicon carbide tube inclined at 4.4 degrees
with respect to the horizontal and had a 76 cm hot zone. The tube rotated at 6 rpm
to provide a residence time in the kiln of about 5 minutes. The product exited the
kiln into room temperature air where it was collected in a metal container and allowed
to cool to room temperature.
General Procedure II for Making the Abrasive Grains
[0077] This General Procedure II was essentially the same as General Procedure I, except
that the original sol contained, in addition to the alumina sol, a zirconia sol. The
average zirconia particle size in the zirconia sol was between about 5 and about 10
nm. The zirconia sols were about 20% solids (in a 15% concentrate of acetic acid aqueous
solution, pH 3.5) and were purchased from Nyacol Products Inc. of Ashland, MA.
General Procedure III for Making the Abrasive Grains
[0078] The following were charged (with continuous mixing) into an 18.9 l polyethylene lined
steel vessel to form a dispersion, 2269 parts of room temperature deionized water,
45 parts of 16N analytical reagent grade nitric acid, and 643 parts of alpha aluminum
oxide monohydrate powder sold under the trade designation Disperal®. Also added to
this dispersion were the optional modifier salts. These salts were the same as described
above in General Procedure I. The resulting mixture was dispersed at high speed for
three to four minutes using a Giford-Wood Homogenizer Mixer (Greeco Corp., Hudson,
NH). The resulting sol was poured into a 46 cm by 66 cm by 5 cm polyester lined aluminum
tray where it was dried in a forced air oven at 100°C for about 24 hours to a friable
solid. The resulting dried material was crushed using a "Braun" type UD pulverizer
having a 1.1 mm gap between the steel plates to form particles. The particles were
screened between 0.125 to 1 mm screen size. The retained particles were fed into a
rotary kiln to form calcined particles. The kiln was a 16 cm diameter, 140 cm long,
stainless steel tube having a 40 cm 600°C hot zone. The tube was inclined at a 2.4
degree angle with respect to the horizontal. The tube rotated at about 6 rpm to provide
a residence time within the calciner of about 5 minutes. Next, the calcined particles
were fed into a 1400°C rotary kiln. The kiln was an 8.9 cm diameter, 1.3 meter long
silicon carbide tube inclined at 4.4 degrees with respect to the horizontal and had
a 76 cm hot zone. The kiln rotated at 6 rpm to provide a residence time in the kiln
of about 5 minutes. The product exited the kiln into room temperature air where it
was collected in a metal container and allowed to cool to room temperature.
General Procedure for Making the Abrasive Products
[0079] The abrasive grains were utilized in coated abrasive products which were tested for
grinding performance. The coated abrasive products were made according to conventional
coated abrasive-making procedures. A grade 50 abrasive grain was prepared by taking
50% by weight from abrasive grains that passed through a 40 mesh U.S. standard screen,
but remained on a 45 mesh U.S. standard screen. The remaining 50% were abrasive grains
that passed through a 40 mesh U.S. standard screen, but were retained on a 50 mesh
U.S. standard screen. A grade 40 abrasive grain was prepared by taking 100% by weight
of abrasive grains that passed through a 35 mesh U.S. standard screen, but were retained
on a 40 mesh U.S. standard screen. Likewise a grade 36 abrasive grain was prepared
by taking 50% by weight from abrasive grains that passed through a 25 mesh U.S. standard
screen, but remained on a 30 mesh U.S. standard screen. The remaining 50% were abrasive
grains that passed through a 30 mesh U.S. standard screen, but were retained on a
35 mesh U.S. standard screen. The abrasive grains were bonded to vulcanized fibre
backings using conventional calcium carbonate filled phenolic make resin and conventional
calcium carbonate filled phenolic size resins. The make resin was pre-cured by heating
to about 88°C at a rate of about 1.1°C/ minute, and then holding at about 88°C for
about 2 hours. The size resin was cured by heating to about 65°C at a rate of about
1.1°C/ minute, and then holding at about 65°C for about 30 minutes, followed by a
heating to about 99°C at a rate of about 0.6°C/ minute, and then holding at about
99°C for about 12 hours. The abrasive grains were electrostatically coated.
[0080] If the coated fiber disc was to be utilized to grind stainless steel, a supersize
coating was applied over the size coat. The supersize comprised (by weight) 14.3 parts
bisphenol A epoxy resin (EPON 828 obtained from Shell Chemical Co., Houston, TX);
9.4 parts polyamide curing agent (Versamid 125 from Henkel Corp., Gulph Mills, PA);
71.25 parts KBF
4; 1.9 parts thickening agent (Cab-o-sil from Cabot Corp., Kokomo, IN); and 3.1 parts
iron oxide filler. The supersize coating was deposited from an organic solvent and
then heated to cure.
Test Procedure I
[0081] The coated abrasive disc was mounted on a beveled aluminum back-up pad and used to
grind the face of a 1.25 cm by 18 cm 1018 mild steel workpiece. The disc was driven
at 5,500 rpm while the portion of the disc overlaying the beveled edge of the back-up
pad contacted the workpiece at about a 7 kg load. Each disc was used to grind a separate
workpiece for a one-minute interval for a total time of 12 minutes. The initial cut
was the amount of metal removed in the first minute of grinding. Likewise, the final
cut was the amount of material removed in the last minute of grinding and the total
cut was the summation of the amount removed throughout the test. For most of the examples,
the performance of the abrasive grain is stated as percent of the Comparative, that
is the total amount of metal removed for the Comparative example was equated to 100%
and the abrasive grain of the examples was measured relative to the 100%. There were
approximately four discs per Example tested. The error associated with each Test Procedure
described herein was about ±5%.
Test Procedure II
[0082] The Test Procedure II was essentially the same as Test Procedure I, except that the
test endpoint was when the amount of metal removed in a one-minute time interval was
less than one-third the value of the initial cut.
Test Procedure III
[0083] The Test Procedure III was essentially the same as Test Procedure I, except that
the test endpoint was 20 minutes.
Test Procedure IV
[0084] The Test Procedure IV was essentially the same as Test Procedure I, except that the
workpiece was 304 stainless steel, and the test endpoint was 10 minutes.
Test Procedure V
[0085] The Test Procedure V was essentially the same as Test Procedure I, except that the
test endpoint was 15 minutes.
Comparative Example A and Examples 1 and 2
[0086] This set of examples compared various abrasive grain compositions. The results can
be found in Tables 1 and 2, below.
Comparative Example A
[0087] The abrasive grains were made according to the teachings of U.S. Patent No. 4,881,951.
The abrasive grains were made according to the sol-gel method and had a composition
of 94.7% alumina, 2.7% lanthanum oxide, 1.3% magnesium oxide, and 1.3% yttrium oxide.
Example 1
[0088] The abrasive grains for this Example were made according to General Procedure I and
there were multiple impregnation steps for this example. The calcined alumina particles
were impregnated three separate times with a zirconyl acetate aqueous solution, and
then the resulting particles were impregnated for an additional four times with an
aqueous solution that contained magnesium nitrate, yttrium nitrate, and lanthanum
nitrate. The resulting abrasive grain comprised by weight: about 86.7% alumina, about
8% zirconia, about 1.3% yttria, about 1.3% magnesium oxide, and about 2.7% lanthanum
oxide.
Example 2
[0089] The abrasive grain for Example 2 was made in the same manner as Example 1, except
that the zirconyl acetate was replaced with zirconyl nitrate.
Table 1.
Test Procedure I |
Example |
Initial cut, g |
Total cut, % of Comparative A |
Comparative A |
83.8 |
100 |
1 |
95.4 |
127 |
Table 2.
Test Procedure II |
Example |
Initial cut, g |
Total cut, of Comparative A |
Comparative A |
88.3 |
100 |
1 |
87.1 |
134 |
2 |
87.3 |
107 |
Comparative Example A and Examples 3 through 7
[0090] This set of examples compared various abrasive grain compositions. The test results
can be found in Tables 4 and 5, below. The results listed in Table 4 were for grade
50 fibre discs and the results listed in Table 5 were for grade 36. For Examples 3
through 7, the abrasive grains were made according to General Procedure I, and there
was a single impregnation step for the examples. The impregnation solution contained
lanthanum nitrate, magnesium nitrate, yttrium nitrate, and zirconyl acetate. The amounts
of these materials were selected to give the sintered abrasive grain compositions
described below in Table 3, below.
Table 3.
Compositions for Examples 3 through 7 |
Example |
%Al2O3 |
%La2O3 |
%Y2O3 |
%MgO |
%ZrO2 |
3 |
94.2 |
2.7 |
1.3 |
1.3 |
0.5 |
4 |
93.7 |
2.7 |
1.3 |
1.3 |
1.0 |
5 |
92.7 |
2.7 |
1.3 |
1.3 |
2.0 |
6 |
91.7 |
2.7 |
1.3 |
1.3 |
3.0 |
7 |
90.7 |
2.7 |
1.3 |
1.3 |
4.0 |
Table 4.
Test Procedure III |
Example |
Initial cut, g |
Total cut, % of Comparative A |
Comparative A |
53.2 |
100 |
3 |
53.3 |
120 |
4 |
65.6 |
129 |
5 |
55.0 |
125 |
6 |
58.0 |
123 |
7 |
55.6 |
120 |
Table 5.
Test Procedure I |
Example |
Final cut, g |
Total cut, % of Comparative A |
Comparative A |
80.9 |
100 |
3 |
88.6 |
104 |
4 |
94.7 |
104 |
5 |
93.7 |
110 |
6 |
91.8 |
102 |
Control Example A and Examples 8 through 14
[0091] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 36. The test results can be found in Table 7, below. For
Examples 8 through 14, the abrasive grains were made according to General Procedure
I and there was a single impregnation step for this example. The impregnation solution
contained lanthanum nitrate, magnesium nitrate, cerium nitrate, yttrium nitrate, and
zirconyl acetate. The amounts of these materials were selected to give the sintered
abrasive grain composition described below in Table 6.
Table 6.
Compositions for Examples 8 through 14 |
Ex. |
%Al2O3 |
%La2O3 |
%Y2O3 |
%MgO |
%ZrO2 |
%CeO2 |
8 |
94 |
2.7 |
0 |
1.3 |
1 |
1 |
9 |
93 |
2.7 |
0 |
1.3 |
1 |
2 |
10 |
92 |
2.7 |
0 |
1.3 |
1 |
3 |
11 |
95 |
2.7 |
0 |
1.3 |
1 |
0 |
12 |
94 |
2.7 |
1 |
1.3 |
1 |
0 |
13 |
93 |
2.7 |
2 |
1.3 |
1 |
0 |
14 |
92 |
2.7 |
3 |
1.3 |
1 |
0 |
Table 7.
Test Procedure I |
Example |
Initial cut, g |
Final cut, g |
Total cut, % of Comparative A |
Comparative A |
64.6 |
64.5 |
100 |
8 |
63.7 |
77.8 |
105 |
9 |
68.1 |
79.7 |
110 |
10 |
64.0 |
80.1 |
111 |
11 |
68.6 |
77.9 |
109 |
12 |
64.8 |
86.1 |
112 |
13 |
71.2 |
84.7 |
115 |
14 |
71.5 |
84.3 |
113 |
Examples 15 through 26
[0092] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 50. The test results can be found in Tables 8 through 11,
below. For Examples 15 through 26, the abrasive grains were made according to General
Procedure II, and there was a single impregnation step for these examples. The impregnation
solution contained lanthanum nitrate, magnesium nitrate, and yttrium nitrate. The
amounts of these materials were selected to give the sintered abrasive grain composition
described below in Table 8. For Examples 15, 17, 19, 21, 23, and 25, the zirconia
sol was stabilized with acetic acid and had a pH of 3.5. For Examples 16, 18, 20,
22, 24, and 26 the zirconia sol was stabilized with nitric acid and had a pH of 0.5.
(Examples 25 and 26 are not within the present set of claims.)
Table 8.
Compositions for Examples 15 through 28 |
Example |
%Al2O3 |
%La2O3 |
%Y2O3 |
%MgO |
%ZrO2 |
15 |
82.9 |
2.7 |
1.3 |
1.3 |
11.8 |
16 |
82.9 |
2.7 |
1.3 |
1.3 |
11.8 |
17 |
93.9 |
2.7 |
1.3 |
1.3 |
0.8 |
18 |
93.9 |
2.7 |
1.3 |
1.3 |
0.8 |
19 |
93.1 |
2.7 |
1.3 |
1.3 |
1.6 |
20 |
93.1 |
2.7 |
1.3 |
1.3 |
1.6 |
21 |
91.5 |
2.7 |
1.3 |
1.3 |
3.2 |
22 |
91.5 |
2.7 |
1.3 |
1.3 |
3.2 |
23 |
88.5 |
2.7 |
1.3 |
1.3 |
6.2 |
24 |
88.5 |
2.7 |
1.3 |
1.3 |
6.2 |
25 |
78.0 |
2.7 |
1.3 |
1.3 |
16.7 |
26 |
78.0 |
2.7 |
1.3 |
1.3 |
16.7 |
Table 9.
Test Procedure I |
Example |
Initial cut, g |
Final cut, g |
Total cut, % of Comparative A |
Comparative A |
81.3 |
68.6 |
100 |
15 |
93.8 |
61.6 |
106 |
16 |
93.1 |
83.0 |
116 |
Table 10.
Test Procedure III |
Example |
Initial cut, g |
Final cut, g |
Total cut, % of Comparative A |
Comparative A |
59.1 |
32.1 |
100 |
17 |
63.0 |
39.1 |
109 |
18 |
58.5 |
43.3 |
105 |
19 |
61.4 |
35.2 |
111 |
20 |
59.6 |
31.4 |
96 |
Table 11.
Test Procedure III |
Example |
Initial cut, g |
Final cut, g |
Total cut, % of Comparative A |
Comparative A |
62.5 |
30.6 |
100 |
21 |
66.7 |
62.1 |
129 |
22 |
65.1 |
62.7 |
127 |
23 |
64.9 |
56.9 |
129 |
24 |
66.7 |
58.3 |
126 |
Table 12.
Test Procedure III |
Example |
Initial cut, g |
Final cut, g |
Total cut, g |
15 |
66.6 |
50.8 |
1390 |
16 |
66.8 |
47.4 |
1423 |
25 |
68.1 |
36.5 |
1367 |
26 |
65.3 |
37.2 |
1311 |
Examples 27 through 30
[0093] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 36. The test results can be found in Table 14, below. For
these examples, the abrasive grains were made according to General Procedure I and
there was a single impregnation step for these examples. The impregnation solution
contained lanthanum nitrate, magnesium nitrate, yttrium nitrate, and zirconyl acetate.
The amounts of these materials were selected to give the sintered abrasive grain composition
described below in Table 13, below.
Table 13.
Compositions for Examples 27 through 30 |
Example |
%Al2O3 |
%La2O3 |
%Y2O3 |
%MgO |
%ZrO2 |
27 |
92.0 |
3 |
1 |
3.5 |
0.5 |
28 |
91.5 |
3 |
1 |
3.5 |
1 |
29 |
90.5 |
3 |
1 |
3.5 |
2 |
30 |
89.5 |
3 |
1 |
3.5 |
3 |
Table 14.
Test Procedure I |
Example |
Initial cut, g |
Final cut, g |
Total cut, g |
27 |
73.9 |
83.1 |
974 |
28 |
71.9 |
87.6 |
999 |
29 |
81.3 |
76.9 |
981 |
30 |
75.6 |
81.2 |
1001 |
Examples 31 through 36
[0094] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 40. The test results can be found in Table 15, below. For
these examples, the abrasive grains were made according to General Procedure II and
the impregnation solution contained the nitrate salt of a rare earth and magnesium
nitrate. For Example 31, the rare earth was dysprosium. Example 32 was gadolinium;
Example 33 was lanthanum; Example 34 was neodymium; Example 35 was praseodymium; and
Example 36 was samarium. The sintered abrasive grain for this set of examples contained
92.7% alumina, 2% zirconia, 2.7% rare earth oxide, 1.3 yttria, and 1.3% magnesium
oxide.
Table 15.
Test Procedures I and IV |
Example |
Procedure I |
Procedure IV |
|
Total cut, g (1018 Steel) |
Total cut, g (304 Stainless Steel) |
31 |
967 |
152 |
32 |
935 |
160 |
33 |
948 |
177 |
34 |
1130 |
190 |
35 |
1097 |
101 |
36 |
972 |
171 |
Examples 37 through 40
[0095] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 50. The test results can be found in Table 17, below. For
these examples, the abrasive grains were made according to General Procedure II and
there was a single impregnation step for these examples. The impregnation solution
contained lanthanum nitrate, yttrium nitrate, and magnesium nitrate. The amounts of
these materials were selected to give the sintered abrasive grain composition described
below in Table 16.
Table 16.
Compositions for Examples 37 through 40 |
Example |
%Al2O3 |
%La2O3 |
%Y2O3 |
%MgO |
%ZrO2 |
37 |
94 |
2.7 |
1.3 |
0 |
2 |
38 |
93.6 |
2.7 |
1.3 |
0.4 |
2 |
39 |
93.25 |
2.7 |
1.3 |
0.75 |
2 |
40 |
92.7 |
2.7 |
1.3 |
1.3 |
2 |
Table 17.
Test Procedures IV and V |
Example |
Total cut, g (1018 Steel) |
Total cut, g (304 Stainless Steel) |
37 |
1250 |
165 |
38 |
1212 |
200 |
39 |
1306 |
238 |
40 |
1251 |
200 |
Comparative Example B and Example 41
[0096] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 40. The test results can be found in Table 18. Control Example
B was made according to Example 38 of U.S. Patent No. 4,314,827. Example 41 was made
according to General Procedure for Making the Abrasive Grains III. The sintered abrasive
grain composition for Example 41 was 84% alumina, 5% magnesium oxide, 6% cerium oxide,
and 5% zirconia.
Table 18.
Test Procedure I |
Example |
Initial cut, g |
Final cut, g |
Total cut, % of Comparative B |
Comparative B |
97 |
60 |
1112 |
41 |
95 |
88 |
1230 |
Comparative Example C and Examples 42 through 45
[0097] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 50. The test results can be found in Table 19, below. Comparative
Example C was made according to the teachings of U.S. Pat. No. 4,881,951 (impregnation
procedure) and contained 96% alumina, 1% lanthanum oxide, 1% neodymium oxide, 1% magnesium
oxide, and 1% yttria. Examples 42 through 45 were made according to General Procedure
for Making Abrasive Grains IV. The sintered abrasive grain composition for Examples
42 and 43 were 96% alumina, 2.5% zirconia, 1% lanthanum oxide, 1% neodymium oxide,
1% magnesia, and 1% yttria. The sintered abrasive grain composition for Examples 44
and 45 were 96% alumina, 2.5% zirconia, 1% lanthanum oxide, 1% neodymium oxide, 1%
magnesium oxide, and 1% yttria. Note that for Examples 42 and 44 zirconia sol contained
acetic acid to stabilize the sol, while each of Examples 43 and 45 utilized nitric
acid to stabilize the sol.
Table 19.
Test Procedure III |
Example |
Initial cut, g |
Final cut, g |
Total cut, g |
Comparative C |
74 |
16 |
1271 |
42 |
87 |
38 |
1694 |
43 |
84 |
36 |
1553 |
44 |
77 |
44 |
1541 |
45 |
84 |
6 |
1380 |
Comparative Examples D and E and Example 46
[0098] This set of examples compared various abrasive grain compositions. The abrasive grains
were screened to a grade 50. The test results can be found in Table 20, below. Comparative
Example D was made according to the teachings of U.S. Pat. No. 4,314,827 and contained
93% alumina and 7% magnesium oxide. Comparative Example E was made according to the
teachings of U.S. Pat. No. 4,314,827 and contained 90% alumina, 5% zirconia and 5%
magnesium oxide. Example 46 was made according to the General Procedure III for Making
the Abrasive Grains. The abrasive grain contained 5% zirconia, 1.3% magnesium oxide,
1.3% yttria, 2.7% lanthanum oxide, and 89.7% alumina.
Table 20
Example |
Total cut, grams |
Comparative D |
927 |
Comparative E |
982 |
46 |
1016 |
[0099] It was also observed by X-Ray Diffraction that the zirconia present in Example 46
was 100% in the tetragonal form. For Control Example E, the zirconia present was 70%
in the tetragonal and 30% in the monoclinic. The tetragonal is the preferred form
and it is believed that it is responsible for the increase in performance.
[0100] The abrasive grain examples described above exhibited the hardness and toughness
values listed in Table 21, below. The procedures used for measurement were as referenced
above in the text.
[0101] Specifically, for both the microhardness and the toughness measurements, abrasive
grains were mounted in a conventional molding compound (commercially available under
the trade designation "EPOMET" from Buehler, Ltd. of Evanston, IL) in 2.5 cm (1 inch)
diameter stainless steel mold rams. The grains and the molding compound were then
pressed at 27.6 MPa (4000 psi) and simultaneously heated to about 150°C in a conventional
mounting press (commercially available under the trade designation "BUEHLER PNEUMET
I MOUNTING PRESS" from Buehler, Ltd.). The molding compound was then cured by holding
it at about 150°C for about 5 minutes. The cured molding compound was then cooled
to room temperature.
[0102] The mounted abrasive grains were then polished using a polishing unit (commercially
available under the trade designation "DIALOG" from Buehler, Ltd.) having a microprocessor
control that dispenses abrasive slurries to the polishing area (commercially available
under the trade designation "METLAP I" from Buehler, Ltd.). The polishing was done
in the following successive stages:
Stage 1
- Polishing surface:
- alumina platen, 20.3 cm diameter (commercially available under the trade designation
"METLAP 10" from Buehler, Ltd.)
- Abrasive Type & Size:
- 30 micrometer diamond slurry (commercially available under the trade designation "METADI
DIAMOND SLURRY" from Buehler, Ltd.)
- Polishing Time:
- 3 minutes, or until the surface is flat
- Force:
- 22.2N/sample (5 pounds/sample)
- Speed setting:
- 240 rpm
- Dispensing sequence:
- 1 second spray on; 10 spray off
- Relative rotation:
- clockwise
Stage 2
- Polishing surface:
- polishing cloth (commercially available under the trade designation "TEXMET POLISHING
CLOTH" from Buehler, Ltd.) clamped on a 20.3 diameter aluminum platen (commercially
available under the trade designation "METLAP" from Buehler, Ltd.).
- Abrasive Type & Size:
- 6 micrometer diamond slurry (commercially available under the trade designation "METADI
DIAMOND SLURRY" from Buehler, Ltd.)
- Polishing Time:
- 10 minutes
- Force:
- 22.2N/sample (5 pounds/sample)
- Speed setting:
- 120 rpm
- Dispensing sequence:
- 1 second spray on; 10 spray off
- Relative rotation:
- counterclockwise
Stage 3
- Polishing surface:
- polishing cloth ("TEXMET POLISHING CLOTH") clamped on a 20.3 diameter aluminum platen
("METLAP")
- Abrasive Type & Size:
- 1 micrometer diamond slurry (commercially available under the trade designation "METADI
DIAMOND SLURRY" from Buehler, Ltd.)
- Polishing Time:
- 30 minutes
- Force:
- 22.2N/sample (5 pounds/sample)
- Speed setting:
- 120 rpm
- Dispensing sequence:
- 1 second spray on; 10 seconds spray off
- Relative rotation:
- clockwise
[0103] The Vickers microhardness of the abrasive grains were measured using a conventional
microhardness tester with a diamond indenter (commercially available under the trade
designation "MINILOAD 2 MICROHARDNESS TESTER" from Leitz of Germany). The indenter
(a highly polished pointed square pyramidal diamond with a face angle of 136 degrees)
was brought into contact gradually and smoothly with the sample to be measured. The
predetermined load was 500 grams. The average of 20 measurements for each example
are provide in Table 21, below.
[0104] The toughness measurement was made using the same instrument as described above for
the Vickers microhardness measurement, wherein a predetermined load was applied to
the sample to be tested causing cracks to generate at the apex of the diamond shape
impression of the indenter. The toughness would be determined using the following
equation:
wherein c is the crack radius, F
N is the indentor load, and β is the semi-apical angle of the indenter (68 degrees
for a Vickers diamond). The average of 20 measurements for each example are provided
in Table 21, below. Further, Table 21 provides the density of the abrasive grain,
as measured with a Micromeritics AccuPyc (Norcross, GA) 1330 pycnometer.
Table 21.
Density, Hardness and Toughness of Selected Examples |
Example |
Density, g/cm3 |
Hardness, GPa |
Toughness, MPa.m½ |
Comparative A |
3.85 |
19 |
3.6 |
Comparative D |
3.57 |
16 |
|
Comparative E |
3.87 |
18 |
|
1 |
4.04 |
22.3 |
4.4 |
3 |
3.92 |
22.1 |
4.1 |
4 |
3.91 |
22.1 |
4.1 |
5 |
3.90 |
22.3 |
4.3 |
6 |
3.91 |
22.3 |
4.3 |
7 |
3.91 |
22.3 |
4.4 |
8 |
3.93 |
|
|
9 |
3.93 |
|
|
10 |
3.94 |
|
|
11 |
3.91 |
21.4 |
|
12 |
3.96 |
21.7 |
|
13 |
3.99 |
22.2 |
|
14 |
3.99 |
22.1 |
|
15 |
4.09 |
22.6 |
4.1 |
16 |
4.08 |
22.6 |
4.0 |
17 |
3.98 |
22.2 |
4.1 |
18 |
3.98 |
22.2 |
4.0 |
19 |
3.98 |
22.3 |
4.1 |
20 |
3.99 |
22.2 |
4.1 |
21 |
4.01 |
22.7 |
4.1 |
22 |
3.98 |
22.6 |
4.1 |
23 |
4.03 |
22.8 |
4.1 |
24 |
4.04 |
22.4 |
4.0 |
25 |
4.11 |
22.5 |
4.2 |
26 |
4.10 |
22.3 |
4.1 |
29 |
3.94 |
|
|
30 |
3.93 |
|
|
31 |
3.93 |
|
|
32 |
3.89 |
|
|
46 |
4.03 |
22 |
|
[0105] Various modifications and alterations of this invention will become apparent to those
skilled in the art without departing from the scope of this invention, and it should
be understood that this invention is not to be unduly limited to the illustrative
embodiments set forth herein.